ab=（cosx+sinx）^2-2sin^2x=sin2x+1-2sin^2x=sin2x+cos2x
=√2sin（x+π/4）
∴f（x）=√2sin（x+π/4）+1
T=2π/1=2π
（Ⅱ）∵x∈[0,π/2]
∴x+π/4∈[π/4,3π/4]
∴f（x）min=√2×√2/2+1=2
f（x）max=√2×1+1=1+√2